The invention relates to a coating process to coat a component having a surface and a passageway that opens out into an aperture on the surface. The invention furthermore relates to an apparatus to implement this coating process.
EP 0 253 754 A1 describes a coating process. A turbine blade, at the surface of which cooling holes open, is coated. During coating of the surface, closure of these cooling holes is prevented by closing each with a plug prior to coating. Such a plug prevents the coating material from penetrating into the cooling hole.
The object of the invention is to define a coating process that avoids blocking or unacceptable narrowing of a passageway aperture. A further object of the invention is to define an apparatus to implement this coating process.
According to the invention, the process-related object is attained by a coating process for coating a component, which has a surface and a passageway that opens out at an aperture on the surface, whereby a coating material is applied to the surface and at the same time a fluid is directed through the passageway and out of the aperture, and whereby the fluid is preheated prior to being directed out of the aperture, particularly to a temperature ranging between 100xc2x0 C. and 900xc2x0 C., preferably between 400xc2x0 C. and 700xc2x0 C.
Such a coating process prevents the passageway from being blocked by coating material during the coating operation or from being undesirably narrowed at the aperture. This is achieved in that the fluid flowing out of the aperture at least partially displaces the coating material. This prevents larger amounts of coating material from getting into the aperture, A suitable adjustment of the pressure at which the fluid flows out of the aperture makes it possible to regulate to what extent the coating material is being displaced by the fluid. It is thus possible to influence the amount of coating material being deposited at the mouth of the passageway, i.e. to influence the coating thickness that forms there. In addition, preheating the fluid prevents the formation of locally cooled areas due to the fluid around the cooling passageway apertures, or cooling of the entire gas turbine blade. A non-preheated fluid, which would cause at least local cooling of the gas turbine blade could thus lead to defects in the layer structure of the coating. For as a rule, a gas turbine blade is kept at a high temperature during the coating operation to improve the quality of the coating.